The present invention relates to devices known as transducers which provide an electrical signal output or indication, when connected in a circuit, of a mechanical or other physical non-electrical input such as motion or force to provide an interface between a physical or mechanical system and an electrical circuit.
Devices of this type are employed where it is desired to provide an electrical indication of a physical quantity to be monitored or measured on a continuous or running basis without the need to record values and reset or restart the measuring device. In particular, transducers are employed to provide an indication of motion or continuously varying displacement. In certain applications, it is desired to have user-effected movement of a control member as the mechanical input with an electrical signal as the output which has the characteristics thereof varied or changed, so as to provide a discrete electrical indication of different positions of the member.
Known movement or displacement transducers have utilized potentiometers and variable resistors employing wipers moved over stationary resistance material to vary the overall resistance of the device. Typically, the variable resistance device is connected in one leg or arm of a Wheatstone bridge circuit. This electrical bridge arrangement provides the desired electrical sensitivity to small changes in resistance representative of a small displacement of the input member to thereby provide the desired accuracy of measurement or control. Alternatively, a microcomputer can be used with a lookup table of predetermined relationships between the property measured or displacement being tracked and the electrical resistance.
However, variable wiper type potentiometers have inherent disadvantages in that they are expensive to fabricate and subject to variation in the electrical resistance due to changes in the wiping surfaces and degradation over time in service. Accordingly, it has been desired to provide a motion or displacement transducer which has a high degree of sensitivity to small displacements and which provides a reliable and repeatable electrical signal and which is low in manufacturing cost.